**1. Introduction**

Even wine contains a low level of proteins and glycoproteins, which usually ranged from 15 to 230 mg/L, proteins present an important role from a technological point of view [1]. Indeed, proteins greatly affect wine quality by contributing to its sensory and foam characteristics [2–4]. However, specific wine proteins, mainly grape wine unstable proteins, can be gradually denatured and aggregate/precipitate during wine storage, developing a light-dispersing haze, this being the main cause of post-bottling haze development in white wines [5]. Even the formation of protein haze is improbable to affect the olfactory or gustatory wine characteristics, turbid wines are usually rejected by consumers, causing significant economic losses for the wine industry and brand image [6–8]. Wine proteins are mainly derived from grapes, but they could also be formed by the metabolism of the several microorganisms (yeasts and lactic acid bacteria) present in the vinification process [9]. Most of these proteins are extinct after wine alcoholic fermentation and consequent fining processes. Nevertheless, the so-called pathogen-related (PR) proteins (β-glucanases, chitinases, thaumatin-related proteins) can persist in the final wine as they are resistant to proteolysis and low pH [10]. They are produced by the grapevine for defence against bacterial or fungal infections and in reaction to abiotic stress [11]. These proteins are resistant to the wine acid conditions, heat and proteolysis due to

their compact structures [9]. Numerous research works have stated that wine total protein levels could not predict wine protein instability, as individual protein fractions synthesised in grape berries are responsible for haze development [12, 13]. Furthermore, the wine chemical composition such as metal ions, ionic strength, pH, alcohol level, polysaccharides and phenolic concentration could also play an essential role in protein haze development as these parameters might affect protein denaturation [8, 14]. Additionally, Pasquier et al. [15] mentioned that the climatic changes, with the rise in temperatures and the reduction in precipitation throughout the grape maturation phase, lead towards increase in the probability of wine protein instability. In the winemaking industry to avoid this instability, normally the unstable proteins are removed through bentonite fining before wine bottling. However, this fining agent is non-specific, removing other wine compounds besides unstable proteins, which may affect wine sensory qualities [16]. Therefore, in the previous years, several alternative solutions to bentonite fining for this aim have been searched [16, 17].
